Me no likey the heat. Especially with humidity. I can't do it anymore. I get very sick way too quick to enjoy anything outside in the summer. So yeah, for me 90 degrees is hot enough to say too hot. Even 85 degrees is hot if I'm in it long enough.
I have adrenal insufficiency which means if I start sweating like a bastard, I lose salt and I deplete my cortisol reserve and I can end up in a bad way quickly. It's happened before and it's why I avoid going outside in the peak of summer. If I have to be in the heat for whatever reason, I take some cold Sprite/7-Up/Sierra Mist and mix it with table salt and drink it regularly to keep my salt level up as I'm sweating. It tastes about like it sounds, but it works. If that fails and it's still too hot and I'm heading south, I carry a Dexamethasone emergency injection to reverse an adrenal crisis. If that fails, it's time for IV steroids and usually an overnight stay in a hospital until my vitals are stable enough to go home and then I'll double my regular daily steroid dose for a week to compensate and then taper it back down to the regular dosage of it.